I couldn't find anything on the topic in the FAQs so now I'm trying here: Is there any theoretical size limit on a fusor?

I'm not talking about making a fusor the size of my house, but rather a fusor the size of a munchkin. I'm sure there is a simple answer out there, but is there anything to the size of the reactor chamber - maybe volume of deuterium present - that makes a standard sized fusion more possible than at a small size? I know that the actual nuclear fusion occurs in an area that is extremely small relative to the rest of the chamber, but I don't know the kind of volume of deuterium needed.

With all the fusors built in the last 15 years it has been extremely difficult to narrow down the size and shape of a fusor vs. efficiency. I started a tread called Fusion reactors by energy quotient, but to date there is not enough data to make any sense of it. Richard stands by his 6" spherical fusor design, but we frankly don't know if it is an optimal size. Then there is the issue of grid size vs shell size, even this has not been firmly optimised as fas as I have seen.

Amateur fusor building is largely an uncoordinated individual effort, which does not produce a quick answer to simple questions like the one you have asked, yet a coordinated effort could easily answer the question, all it takes is to build 5-10 identical chambers and run them under the same conditions to see how the fusion rate scales with size, but AFAIK no one has done it.

As noted in my FAQ above and talked about in Steven's post. Definitive results are pretty much non-extant here on size, shape and grid to chamber volume ratios. I doubt there is such a thing as a theoretical limit to the size a working fusor might be constructed. I am also rather confident that monsters the size of a continent would remain forever as inefficient as a 4" fusor, but with unbelievably more fusion going on per unit time in the device. It's that efficiency issue that kills the fusor, be it made in a 4" tee or a 500 foot diameter sphere.

It all falls back to how much money you have on hand and how agressive you are in nailing down the data. With a highly concerted effort by one person who has already built at least one significant fusor and about 50,000 - 100,000 dollars spent in a thrifty manner, I think that person could reliably answer a lot of your questions in a couple of years of work and research. At the end of that effort, there would be a whole bunch of now dormant "lesser" fusors for use as planter pots. You would know for sure, about how big and in what form a fusor of significant fusion capability, compared to those preceeding it, might be constructed and have a handle on the final costs. Still, in the end you would just have a great fusor producing far less than 10e8 fusions per second costing maybe $25,000 for the thrifty would-be fusioneer.

Not one being who ever landed here was in that class, monetarily, or who also packed the gear needed to accomplish the task. Most of those of us who have been successful realize a full order of magnitude better than 10e6 fusions/sec would require a full order of magnitude more money to complete and achieve no real superiority other than braging rights, king-of-the-hillism recognition.

What we do know is that more volume means more fusion fuel available for fusion and, thereby, gas loss in the flowing gas regime... (more money...wasted deuterium).

The larger gas volume obtained above means much more money for a vacuum or fusion chamber regardless of shape.

Finally, this is a serious amateur effort, undertaken with obviously smallish amateur purses ( a few thousand for the most successful here). The vast majority of those seemingly so inspired to build their own fusion reactor often present themselves with knowledge and skill sets which are pretty close to zero. The number of new supposed fusioneer aspirants versus successful fusioneer ratio of late is appallingly large due to the DIY crowd stumbling in here, virtually none of whom pack the gear needed for a win.

It would wonderful to put a nice little package of precise answers to your original query, but the serious amateur's here can only supply the limited, yet hard won knowledge obtained though the doing of hands-on work. We can supply caveats and warn of blind alleys and how we have lost treasure in past follies so that you might proceed along a more well worn, but sure path.

In the end, if you think big, have really big, big money on hand to blow, as it will flow through your hands like water through a coarse sieve.

Richard Hull

Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

There is another size limit for the chamber, which seems to be the vacuum pumps and the cost of them.
If you take a professional vacuum chamber with 1 m³ volume you will need several pumps (eg. 10-15) with a price of about 10.000 per piece.
The bigger the chamber becomes the more difficult it is to control leaks. So I think it is just a matter of price and complexity.

Just so I understand everything, a large fusor would not gain any efficiency over a smaller one. But would a very small fusor lose any efficiency compared to a not-quite-so-small-one? Would the only real downside to a 1" fusor be that it would be impossible to measure neutron counts?

Werner Engel wrote:… to be precise: I’m talking about turbo pumps reaching 10e-8 mbar or better. I know that’s not normal fusor pressure regime, but for tokamaks that’s fine and a good situation to start.

I have a pretty decent sized chamber, 24" x 30" with a 2000l/s turbo that's pretty necked down and it gets down to that just fine. Within a few minutes of starting the turbo it will be down to the -6 range.